Before departing on the initial parachute jumping flight the pilot dipped sticked both tanks and determined that they contained 23 gallons of fuel. The pilot inaccurately calculated that there would be enough fuel to conduct the initial and second flight before fueling would be required. After the parachute jumper departed the airplane on the second flight and during the normal descent to the airport the airplane sustained a total loss of power. The pilot elected to land in a grape vineyard because the airplane’s altitude was insufficient to negotiate the airport. The airplane struck a unmarked transmission wire and crashed during the emergency landing. The airplane contained about 8 gallons of fuel, the unusable amount for all attitudes.